Luminance contrast and color contrast are key determinants of how easily information on a computer display can be read. FIG. 1 illustrates the visual effects of luminance and color contrast on image clarity and legibility. High levels of contrast produce high levels of image clarity and legibility.
Normal aging has a detrimental effect on visual contrast sensitivity, such that displayed information which is legible to an individual in his/her twenties may not be legible to an individual in his/her forties and older. In addition to the effects of normal aging, there are many medical and genetic factors, such as color blindness and color deficiency, that affect contrast sensitivity and overall visual acuity. As many as 8% of men and 1% of women have some form of color blindness, as disclosed by the American Optometric Association (http://www.aoanet.org/cvc-color-deficiency.html).
Furthermore, § 508 of the Rehabilitation Act of 1973, as amended (29 U.S.C. 794d), requires that when Federal agencies develop, procure, maintain, or use electronic and information technology, Federal employees with disabilities (including visual disabilities) have access to and use of information and data that is comparable to the access and use by Federal employees who are not individuals with disabilities, unless an undue burden would be imposed on the agency.
Companies developing graphical user-interfaces for products sold to the government as well as retail markets have a keen interest in designing these user-interfaces to ensure that they are legible to the general population, including those with visual disabilities.
Presently, graphical user-interface design relies primarily on the subjective judgment of the designer as to whether the degree of visual contrast between text (or other foreground content) and background is sufficient to allow most individuals to read the display content. Various tools are available which allow the designer to choose among Web-Safe colors (Niederst, J., Web Design in a Nutshell. Sebastopol, Calif.: O'Reilly & Assoc., 1999, p. 30), a set of 216 colors so called because they utilize red, green, and blue primary combinations that are less likely to produce dithering on any given display, and view the chosen colors in combination (one such example is VisiBone's Webmaster's Color Laboratory). However, these tools still leave to the subjective judgment of the designer the assessment of whether a given set of foreground and background colors creates sufficient visual contrast, a particularly difficult if not impossible task for a normal sighted designer to do for the portion of the population with visual disabilities. Thus there is a pressing need for a method to objectively evaluate the legibility of foreground/background color combinations, that will consider both luminance and color contrast, and which will address the needs of the visually disabled (especially color-deficient) portions of the population.